Gene expression in eukaryotes is one of the most complex, highly orchestrated processes in living organisms. Numerous studies have shown that steps such as transcription, messenger RNA (mRNA) processing and mRNA decay, are highly coupled, forming an intricate molecular circuit for regulation of protein-coding genes. Central to this process, are a class of RNA helicases called DEAD-box proteins that perform essential roles in all aspects of RNA biology. Dbp2 is a largely uncharacterized member of the DEAD-box RNA helicase family in the budding yeast Saccharomyces cerevisiae. Whereas numerous studies have shown that the human (h) ortholog of Dbp2, hDDX5 or p68, functions as a transcriptional regulator, no transcriptional role has been described for Dbp2 and the precise molecular function of hDDX5 in this process is not understood. Our studies now provide the first demonstration that Dbp2 is required for nuclear gene expression steps in budding yeast, functioning at the interface between mRNA biogenesis and chromatin remodeling. Furthermore, our work demonstrates that Dbp2 functions at sites of non-protein coding RNA synthesis by RNA polymerase II. Herein, we propose to obtain a detailed understanding of Dbp2 using a combination of biochemical, molecular and genetic approaches. In Aim I, we will utilize a series of in vitro assays to biochemically characterize Dbp2 and subsequently analyze the enzymatic requirements for normal cell growth and gene expression. In Aim II, we will determine how Dbp2 functions in gene expression through a combination of molecular and genetic approaches. In Aim III, we will define and characterize the in vivo molecular interactions that enable Dbp2 to 'sense'nascent transcripts. Our long term working model is that Dbp2 is an enzymatic 'toggle'in the gene expression circuit that regulates the transcriptome. Thus, these studies have the potential to reveal novel mechanisms for genome-wide epigenetic regulation, an NIH strategic initiative reflective of the current challenges facing biomedical research. Importantly, numerous DEAD-box protein genes have been linked to human disease states including cancer, neurological disorders and AIDS. Therefore, uncovering the physiological role of individual DEAD-box proteins is a major challenge to basic biological research and the medical community. PUBLIC HEALTH RELEVANCE: The ability to control the expression of specific genes is essential to cellular growth, adaptation and survival. Dbp2/hDDX5 is an RNA helicase enzyme whose over-expression promotes tumor formation and resistance to chemotherapeutics. Knowledge regarding the function of hDDX5 in gene expression is key to defining the underlying molecular basis for cancer and other human diseases.